Hi
Not sure how true this is, but i gotten my winter tires installed from a local shop, anyways, the guy at the shop told me its best i leave my car running a min at lease after i stop driving for the turbo to cool down...I try to leave it running for 20 secs usually because my cousin's friend has a 5 series and i remember he told me the same thing before i even gotten the car.

I'm pretty sure that this used to be true on earlier turbos without intercoolers and even then it was only after the car was run hard. Modern cars with intercooled turbos don't need to be run for any time after stopping. If run hard, you would here my Audi's intercooler run by itself a few minutes after I shut it off. If you were really beating on it, you can run it for a minute or so just to be safe but I have never heard it to be necessary in modern turbos.

The intercooler have nothing to do with this.
The main reason behing letting the engine idle for at least 1 minute on a turbo car after a hard run is the turbo's turbine shaft bearing. If u switch off the engine straight after a hard run, the heat within the turbo will burn off the oil within the shaft assembly as the oil have stopped circulating. By letting the engine idle for a while would've let the turbo cool down, as it's not producing any boost as well as the circulating oil would've taken heat away from shaft bearing.
Unless the oil circuit is designed to continue circulating after switching off the engine, it is still beneficial for the engine to idle a bit before switching off, or u can just drive slowly before parking the car.

Ok, the intercooler, the fans, and everything else you guys are talking about has 0 to do with why modern turbo's no longer need a turbo timer to let the oil cool, so as to not cook it within the bearing.

Modern turbos now use water cooling, along with oil cooling to keep the bearings and turbine cool. When you turn the engine off, the water continues to flow throughout to cool off the bearings which in turn keeps the oil from scorching and sticking, since it is no longer flowing. Old turbo's were mianly oil cooled, so letting it run a little while after a hard run, was to let the oil continue to do its job since it was the only way it cooled off.

So, there is no reason to use a turbo timer with a modern oil/water cooled turbine. Enjoy!

Hi
Not sure how true this is, but i gotten my winter tires installed from a local shop, anyways, the guy at the shop told me its best i leave my car running a min at lease after i stop driving for the turbo to cool down...I try to leave it running for 20 secs usually because my cousin's friend has a 5 series and i remember he told me the same thing before i even gotten the car.

it is not something you have to worry about on our cars. now lets say that you have been running it extremely hard for a good period of time like on a track day where you do numerous laps one after another, then you can let it idle for a minute. even then by the time you get off the track and get to the paddocks, that is usually enough time for the turbo to cool off.

Ok, the intercooler, the fans, and everything else you guys are talking about has 0 to do with why modern turbo's no longer need a turbo timer to let the oil cool, so as to not cook it within the bearing.

Modern turbos now use water cooling, along with oil cooling to keep the bearings and turbine cool. When you turn the engine off, the water continues to flow throughout to cool off the bearings which in turn keeps the oil from scorching and sticking, since it is no longer flowing. Old turbo's were mianly oil cooled, so letting it run a little while after a hard run, was to let the oil continue to do its job since it was the only way it cooled off.

So, there is no reason to use a turbo timer with a modern oil/water cooled turbine. Enjoy!

The turbo on the N20 is oil-cooled (only), not water-cooled. Google "BMW N20 technical specification" and you can find the very detailed BMW documentation on this engine. The N20 does have an oil cooler (oil-to-coolant heat exchanger) that's separate from the turbo, so I suppose you could say that the turbo is *indirectly* water-cooled, but to call it "water cooled" is miss-leading. I don't know if the N55 turbo is oil-cooled, water-cooled, or both.

To the OP: same as others have suggested, my advice (and practice) is, if you have been driving aggressively (generous use of WOT), drive moderately for the last couple minutes before you park (and shut down).

The turbo on the N20 is oil-cooled (only), not water-cooled. Google "BMW N20 technical specification" and you can find the very detailed BMW documentation on this engine. The N20 does have an oil cooler (oil-to-coolant heat exchanger) that's separate from the turbo, so I suppose you could say that the turbo is *indirectly* water-cooled, but to call it "water cooled" is miss-leading. I don't know if the N55 turbo is oil-cooled, water-cooled, or both.

Please re-read what I posted. The TURBINE is WATER and OIL cooled. The oil cooler has nothing to do overall with the turbine. It is an oil cooler. That is all. It is used to cool the oil. Non-turbo engines also have these. Here is the link, page 103, look at the diagram. It shows the passageways of the turbine, and has the numbers below that explaining what each passageway is.

It shows in the picture #2 is the oil inlet, #6 is the oil passageway, and #5 is the cooling passage with #7 being the coolant return line. It does not show the oil return line or the water inlet line, but trust me, they are there. So there is no *indirectly* water cooling going on here, The Turbine is oil and water cooled, like most stock modern turbines are.

Go to your car, lift it up. Look under it. Look at the turbine and you will see the oil inlet at the top of the turbine, an a large outlet at the bottom, which usually goes back into the block or oil pan, depending on the design. Now look at the inside and outside directly to the left and right (but below) of the oil inlet. You will see water lines that go in and out of the turbine. These usually return somewere on the back of the engine, which then of course go through to the radiator to cool the coolant off.

I am currently on my ipad, so sorry I cannot upload the picture here, but like I said above, page 103 of the link has the picture of everything.

Edit: Evidently, this forum does not like outside links. So, Google BMW N20 technical specification, and click on the link labeled 21 Sep 2011 with the above technical training document, as you asked me to do, and scroll to page 103 of that document. You will see what I posted above to be true and correct.

BTW, I have raced turbo engine cars since the early 90's in Japan, and I helped rebuild them also. So yes, I do have a decent amount of experience in this field. I also have a 420HP RX-7 that is my play toy, hence I opted for a 328, not a 335. I stopped the power at 420 since anything above 450 makes the stock transmissions go KABOOM, and aftermarket would cost me in excess of $5-10G for a weekend play toy. I no longer race on a circuit, so there is no need for 500+ HP, although the engine is built to handle it.

Last edited by Kaitain; 11-27-2012 at 05:48 PM.
Reason: URL link not allowed.

Please re-read what I posted. The TURBINE is WATER and OIL cooled. The oil cooler has nothing to do overall with the turbine. It is an oil cooler. That is all. It is used to cool the oil. Non-turbo engines also have these. Here is the link, page 103, look at the diagram. It shows the passageways of the turbine, and has the numbers below that explaining what each passageway is.

It shows in the picture #2 is the oil inlet, #6 is the oil passageway, and #5 is the cooling passage with #7 being the coolant return line. It does not show the oil return line or the water inlet line, but trust me, they are there. So there is no *indirectly* water cooling going on here, The Turbine is oil and water cooled, like most stock modern turbines are.

Go to your car, lift it up. Look under it. Look at the turbine and you will see the oil inlet at the top of the turbine, an a large outlet at the bottom, which usually goes back into the block or oil pan, depending on the design. Now look at the inside and outside directly to the left and right (but below) of the oil inlet. You will see water lines that go in and out of the turbine. These usually return somewere on the back of the engine, which then of course go through to the radiator to cool the coolant off.

I am currently on my ipad, so sorry I cannot upload the picture here, but like I said above, page 103 of the link has the picture of everything.

Edit: Evidently, this forum does not like outside links. So, Google BMW N20 technical specification, and click on the link labeled 21 Sep 2011 with the above technical training document, as you asked me to do, and scroll to page 103 of that document. You will see what I posted above to be true and correct.

BTW, I have raced turbo engine cars since the early 90's in Japan, and I helped rebuild them also. So yes, I do have a decent amount of experience in this field. I also have a 420HP RX-7 that is my play toy, hence I opted for a 328, not a 335. I stopped the power at 420 since anything above 450 makes the stock transmissions go KABOOM, and aftermarket would cost me in excess of $5-10G for a weekend play toy. I no longer race on a circuit, so there is no need for 500+ HP, although the engine is built to handle it.

My bad, I was using the same figure, in the same document, as my reference, but I missed the "cooling passage" and "coolant return" features (both those labels were on the next page, that's my excuse, and I'm sticking with it). And I'm very familiar with oil-to-coolant heat exchangers, I mentioned it because it does cool the oil (separate from the turbo) when the oil is hot (helps warm the oil during warm-up). I was hoping the N20 had an oil-to-air oil cooler, but apparently not.

The N20 has an electric coolant pump, and according to the same document, it will continue to run "...when the engine is stopped and very hot or to cool the exhaust turbochargers." (page 96). Cool